Patients suffering from drug-resistant forms of partial epilepsy undergo special electrophysiological studies to strengthen the basis for possible surgical treatment. Special methods include stereotactically implanted depth electrodes in epileptogenic regions, radiotelemetric and videotape monitoring of seizure activity, chronic microelectrode recordings of neuronal activity and computer analysis of the spread of seizure discharges. The effects of several agents, diazepam, phenobarbital, ketamine, nitrous oxide, thiopental, on the cortical and subcortical EEG activities have been defined. During spontaneous psychomotor seizures large increases in blood flow occur in limbic system sites judged by changes in temperature and oxygen availability. Chronic implantation of microelectrodes in man have realized successful unit recordings for as long as three weeks. Many observations of normal and abnormal regions were correlated with EEG, behavioral states including seizures. Follow-up studies of 82 patients showed three-fourths could benefit from surgical treatment. Neurological, psychiatric and psychological findings are being analyzed. Neuropathological studies of epileptogenic tissues include Golgi stains, electron microscopic preparations, and histochemical stains.